Lights and Display Board Circuits

FL Twilight Switch Schematic Circuit Diagram

This specific light dimmer is tailored for fluorescent lamps (FLs). The circuit is minimalistic, requiring only a few components, and can be accommodated on a compact 2 by 3 cm circuit board when utilizing SMD components. The mains voltage is rectified through D1 to D4, and this waveform is directed to the fluorescent lamp and a thyristor connected in series.

FL Twilight Switch Schematic Circuit Diagram

Automatic Lighting Control: Daytime and Nighttime Operation

During daylight hours, the thyristor remains inactive as it receives no gate current, keeping the lamp switched off. When night falls, a continuous gate current activates the thyristor, ensuring the fluorescent lamp remains fully illuminated. The light/dark detection circuit, comprising components T1 to T4, facilitates this automatic control. This section is powered directly from the rectified mains voltage through R1/D5/C1, enabling precise light detection and response.

Light Sensing and Circuit Operation: T1 to T4 Configuration

Phototransistor T1 gauges ambient light levels. In ample daylight, T1 conducts, causing T2 and T3 to block. Consequently, T4 conducts, preventing gate current from reaching the thyristor. However, as dusk sets in, the voltage across electrolytic capacitor C2 rises. Eventually, T2 and T3 begin to conduct, cutting off T4. Consequently, the thyristor receives continuous gate current through the voltage divider R6/R7/R8, lighting up the lamp. R9 and R10 introduce hysteresis in the switching behavior of T2 and T3, preventing rapid on-off cycles as darkness falls.

Understanding Capacitors: Energy Storage Components

Capacitors are essential electrical components that store energy from a battery. They consist of two metal plates separated by a non-conductive substance. When activated, capacitors release stored electricity almost instantaneously. The capacitance of a capacitor represents the ratio of stored charge to the potential difference between its conductors. This unit of measurement is termed farad, denoted as F in the SI system. Electrical safety precautions are vital when constructing the circuit, given its direct connection to mains voltage.


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